This invention relates to a method of centering rotary drum such as a drum of a VTR rotary drum device.
A VTR rotary drum device comprises an upper drum and a lower drum. For example, the upper drum is a rotary drum and the lower drum is a stationary drum. Some of such upper drums are provided with magnetic heads. VTR rotary drums include the flangeless type rotary drum device shown in FIG. 1 and the flanged type rotary drum device shown in FIG. 2.
The structure of the flanged type rotary drum device shown in FIG. 2 will be briefly explained.
In this figure, the rotary drum device comprises an upper drum 303 and a lower drum 310. The upper drum 303 is fixed to a flange 311 which latter is fixed to a main shaft 305. On the upper drum 303, there are mounted a plurality of magnetic heads 330 and 340.
On the other hand, the lower drum 310 is rotatably mounted on the main shaft 305 by way of bearings 312. Thus, the upper drum 303 is a rotary drum and the lower drum 310 is a stationary drum.
A video signal VS and a drive signal DS are fed to the device. In response to the drive signal DS being fed to a motor 306, the main shaft 305 and the upper drum 303 are rotated by way of the bearings 312.
As a result of a demand for thinner and cheaper rotary drum devices, flangeless type rotary drum devices of the kind shown in FIG. 1 are now becoming the norm.
The structure of the flangeless type rotary drum device shown in FIG. 1 will now be described.
An upper drum D has a bearing housing 159 in which a plurality of bearings 100 are mounted. As a result, the upper drum D is rotatable on the bearings 100 about a main shaft SP with respect to a lower drum UD.
A rotor core 440 of a motor MG is fixed to the upper end of the main shaft SP. A coil 430 is wound around the rotor core 440. The motor drive signal DS is fed to this coil 430.
A plurality of head bases 200 are fixed to the upper drum D and magnetic heads H are mounted on these head bases 200. Further, a rotor core 410 of a rotary transformer 400 is mounted on the upper drum D.
The lower drum UD, on the other hand, is fixed to a base. A stator core 420 of the rotary transformer 400 is fixed to this lower drum UD. The video signal VS is exchanged between the rotor core 410 and the stator core 420 in a non-contact fashion. This arrangement enables the magnetic heads H to record signals on the VTR tape and reproduce signals from the VTR tape.
However, with the flanged type rotary drum device shown in FIG. 2, the upper drum 303 is fixed to a base-like flange 311 in the manner described above. To achieve this, the upper drum 303 is provided with a large diameter hole 313 to accommodate the flange 311.
The internal diameter of this hole 313 is 17 mm for a drum for VHS 8 mm video, for example.
Because the rotation of the upper drum 303 must be highly precise, the concentricity, circularity and perpendicularity of the hole 313 with respect to the external diameter of the upper drum 303 and the surface 340 on which the magnetic heads are mounted must be kept to less within .+-.3 .mu.m.
Consequently, in the process of adjusting the positions of the magnetic heads H and fixing thereof on the upper drum 303 it is necessary to mechanically position the upper drum 303 with the inner diameter of the large hole 313 of the upper drum 303 as a reference using a collet and fix the upper drum 303 after it is so positioned.
In the case of the flangeless type rotary drum device, on the other hand, the bearings 100 are directly mounted inside the bearing housing 159 of the upper drum D.
That is, the bearings 100 are disposed in the internal diameter portion of the upper drum 303 and consequently it is not possible to use a collet to secure the upper drum D in position as is done in the case of the flanged type rotary drum device of FIG. 2.
Therefore, even if the upper drum D is centered using the main shaft SP as a jig, because there is play of, for example, at least 0.5 .mu.m in the bearings 100, in practice it is not possible to center the upper drum D with the required degree of accuracy.
This centering of the upper drum D is extremely important for the adjustment of the mounting positions of the heads H on the upper drum D as described above.
Consequently, with the flangeless type rotary drum device of FIG. 1, especially in the case of an upper drum having bearings, it is necessary to center the upper drum D using the boss of the bearing housing 159 or the outer circumferential portion of the upper drum D as a reference.
Further, as a reference in the height direction (the main shaft SP direction) of the magnetic heads H with respect to the upper drum D, it is necessary to use the magnetic head mounting surface of the upper drum D as a reference. In other words, high precision in the magnetic head height is also required.
Accordingly, it is an object of this invention to provide a rotary drum centering method with which it is possible to precisely perform the drum centering of a rotary drum necessary for adjusting magnetic heads thereon and accurately obtain a reference in the height direction of the magnetic heads, and an apparatus used therefor.
Another object of this invention is to provide a method for centering a rotary drum for positioning of magnetic heads thereon wherein the rotary drum is held in a predetermined position, the position of an outer circumferential portion of the rotary drum is detected by a detector and the centering position of the rotary drum is calculated on the basis of the detected out circumferential portion of the drum.
Still another object of this invention is to provide a method for centering a rotary drum for positioning of magnetic heads thereon wherein the rotary drum is held in a predetermined position and a target portion of the rotary drum concentric with an outer circumferential portion of the rotary drum is pressurized so that the center of the rotary drum coincides with a predetermined reference axis.
A further object of this invention is to provide a method for centering a rotary drum for positioning of magnetic heads thereon wherein the rotary drum is held in a predetermined position and is rotated about a predetermined reference axis and a target portion of the rotary drum which is concentric with an outer peripheral portion of the drum is adjusted via tapping until it is exactly centered with respect to the predetermined axis.
A still further object of this invention is to provide an apparatus for centering a rotary drum for positioning of magnetic heads thereon which apparatus comprises means for holding the rotary drum, a detector for detecting the position of an outer peripheral portion of the rotary drum and means for calculating the center position of the drum as a centering position of the drum.
A yet still further object of this invention is to provide an apparatus for centering a rotary drum for positioning of magnetic heads thereon which apparatus comprises means for holding the rotary drum, means for rotating the rotary drum about a predetermined reference axis and means for tapping a target portion of the rotary drum concentric with the outer peripheral portion of the drum.
With the above constitution, centering of the rotary drum is performed by the detectors detecting the outer circumferential portion of the rotary drum or by using the pressurizing means or the tapping means to center the rotary drum mechanically.